1. INTRODUCTION

In this introductory talk, I shall try to highlight a number of issues
which will be
addressed during the conference. To reduce the risk of trespassing on
the territory
of later speakers, I shall limit myself to general and tentative
remarks. I shall try to
focus on what we can learn about the origin of clusters and
superclusters, emphasizing
that almost all the observations to be discussed at this meeting are relevant
to this issue. There are many classes of astronomical objects whose
properties can
be studied and understood in detail even in ignorance of their
origins. To take an
extreme example, our understanding of solar physics, and the general
structure of
the Sun at the present day, is in no way impeded by uncertainties about how it
formed, or about star formation in general. This is, at least in part,
because the
characteristic timescales in the Sun are very short compared to its age:
the Sun's
dynamical timescale is less than an hour, so the period of solar
oscillations is shorter
by a factor of around 1014 than the Sun's total age. All
dynamical memory of how
the Sun formed was therefore erased long ago, and is irrelevant to our
attempts to
understand its present structure. In contrast, the dynamical timescales
for clusters
and superclusters are not much shorter than the age of the
universe. These systems
therefore retain an imprint of how they formed. Moreover, they are so
bright that we
can observe them out to high redshifts, and therefore at earlier cosmic
epochs when
they were less evolved. Clusters and superclusters tell us about
structures in the
early universe, and the subject of our conference impinges directly on
cosmology.

Our knowledge of clusters and superclusters has expanded greatly within the
last decade. But it is salutary to recall that the subject has a rather
longer history.
Indeed, the classic work of Shapley and Ames in the 1930s had already
delineated
many of the features of the largescale galactic distribution which
exercise us so
much today. From their studies of the distribution of galaxies brighter
than 13th
magnitude, Shapley and Ames were already able, in 1938, to delineate the
Virgo cluster, several concentrations of clusters at
greater distances, and draw attention
to the asymmetry between the northern and southern galactic
hemispheres. Further landmarks in the subject are associated with the
names of Abell, de Vaucouleurs,
Oort, Einasto, and many others. It is on these pioneering foundations
that later
work, including contributions to be reported at this meeting, has been built.